Quick connect couplings have been widely used in the U.S. Automobile industry for many years. Although applicable in numerous applications, quick connectors are typically employed in fuel systems and vapor recovery systems. The simplest and most cost effective design is the plastic housing female type quick connector releasably mated to a metal male tube endform. The opposite end of the female housing most typically defines a stem having a number of axially spaced barbs forms on the outer circumferential surface thereof and a nylon or plastic tubing endform pressed thereover. Such an arrangement is described in U.S. Pat. No. 5,542,712, issued Aug. 6, 1996, entitled "Quick Connector Housing With Elongated Barb resign".
In fluid handling systems, it is imperative that the connectors used have their male and female portions properly coupled together. A faulty connector enables an associated system to leak fluid. This can be particularly disadvantageous when the system is under pressure and the leaking connector expels the pressurized fluid. Furthermore, recent federal legislation has mandated significantly reduced hydrocarbon emissions from automotive fuel and vapor recovery systems. Conventional quick connectors, although effective to mechanically maintain tubing endforms in assembly with their associated connector bodies, have not adequately addressed the federal requirements. Also, the materials employed, typically nylon 12, do not provide sufficient resistance to the permeation of hydrocarbons therethrough.
The permeation problem has been addressed in part through the development of co-extruded multi-layer plastic tube containing two or more discreet layers of different types or formulations of plastic, one of which is specifically designed to provide an effective permeation layer, blocking the escape of hydrocarbons from the system. In general the most successful multi-layer tubing employs a relatively thick outer layer composed of a material resistant to the exterior environment. The innermost layer is thinner and is composed of a material which is chosen for its ability to block defusion of materials, such as hydrocarbons, alchohols and other materials present in fuel blends, to the outer layer and may have a degree of electrical conductivity sufficient to dissipate static charges generated by the flow of fluid therein. To date, it has been extremely difficult to obtain satisfactory lamination characteristics between dissimilar polymer layers. Thus, the use of one or more intermediate layers for bonding the inner aid outer layers has been proposed.
The use of multi-layer tubing in fuel related applications has been problematic inasmuch as the tubing endform necessarily exposes the lamina ends of the inner and outer layers as well as any intermediate layers to either the system fuels and vapors or the equally harsh exterior environment. Such exposure tends to degrade the bonding between the various layers, causing delamination or separation of the layers, resulting in loss of system integrity, fuel contamination and even blockage of fluid flow.
A related problem stems from dual aspects of commercially available quick connect devices, to wit: high volume and low sale price frequently necessitating the use of inexpensive, somewhat pliable materials, and complex contours of extremely small inter-fitting components. These aspects collectively increase the likelihood of misassembly. High volume production techniques, including automated assembly tends to aggravate the problem wherein misassembly or impermissible dimensional variations of the components is difficult to detect. Excessive dimensional tolerance stack-up can result in low pull-apart characteristics between the barbed stem and the plastic tube and produce leakage. Misassembly, such as failure to include a O-ring can also result in leakage. In the case of multi-layer tube, dimensional and/or adhesive problems can result in mechanical delamination upon insertion of the tube over the barbed, stem. Finally, mono-wall plastic tube or multi-layer structures with low hoop strength can relax over time or at elevated temperatures, resulting in leaking or weeping of fluid.